This project involves the development and application of new methodologies to epidemiologic research. (1) The use of randomized recruitment for sampling in case-control studies was further developed: (2) collaborative work continued toward developing methods for handling missing data in case-control studies: (3) the applicability of general risk models for case-control data was shown: (4) a method was developed for adjusting for bias due to a secular trend in opportunity for exposure when analyzing retrospective data on time-to-pregnancy: (5) work continued on designing efficient studies of early pregnancy loss: (6) work was begun on making efficient use of the retrospective data when "disease' status in a case-control study is based on history of failures (versus history of successes); e.g., history of repeated spontaneous abortion.